1. Field of the Invention
This invention relates generally to a seal member interposed between two elements for maintaining fluid-tight connection therebetween, and more particularly to a seal member adapted to be used for a fluid-tight connection between a plastics reservoir and a metal cylinder body.
2. Description of Prior Art
Recently, in order to reduce the weight of a master cylinder assembly, the reservoir portion thereof has been made of plastic material. However, since the cylinder body has to be made of a metal material such as cast iron or aluminum for functional reasons, the two portions having different thermal expansion coefficients must be connected to each other to form a master cylinder assembly. Due to the difference of their thermal expansion coefficients, it is difficult to maintain the fluid-tight connection between the reservoir and cylinder body portions, that is, when the temperature surrounding the master cylinder rises, the plastic reservoir, having a relatively high thermal expansion coefficient, will expand at a greater rate than the metal cylinder having a relatively low thermal expansion coefficient. This results in deformation of the connecting portion of the reservoir and cylinder even if they have been properly connected to each other on assembly.
In order to obviate such a drawback, one improvement has been proposed, wherein a grommet type seal member is inserted between a plastic reservoir and metal cylinder so as to absorb the excess expansion therebetween (British Pat. No. 1,096,007 published on Dec. 20, 1967).
It should be noted, however, that such resilient seal members as rubber or resilient plastics also have high thermal expansion coefficients. Thus, when the grommet type seal member with its entire peripheral (outer and/or inner) surfaces, in sealing contact with the connecting portion of the reservoir and cylinder body is subject to high temperatures, a great deal of thermal stress will be generated at the connecting portion, thereby deforming the plastic reservoir as well as the seal member itself, resulting in a critical defect in the sealing function.